The present invention relates to an image reading device that reads images in an image-forming apparatus such as a facsimile, a copying machine and a printer and images in an image-pick-up device such as a telecamera and others, and more particularly to an image reading device provided with an image-reading unit wherein light images or optical images are read from a document illuminated by means of a solid image-pick-up element (or a solid state image sensor) such as CCD through an optical member such as a dichroic prism or the like.
For example, a color image forming apparatus, especially a color image forming apparatus in a digital system is composed generally of a color image processing device such as an image reading device and an image writing device. The image reading device, for example, separates light images obtained from the document by an exposure scanning, after causing them to pass through the image forming lens system for reading, into a plurality of light by means of a light separating means located behind the image forming lens system. In the case where images are formed on a line image sensor consisting of a solid image-pick-up element that receives light in each channel after separating into red (R) and cyan (C), for example, each line sensor needs to be mounted after the sufficient adjustment of the position and the perpendicularity for each spectral optical axis, so that light images from aforesaid lens system for reading may be formed correctly. Namely, when light images on each line image sensor are not corresponded correctly with each other, it adversely affects the reproduced images reproduced by the writing device. Since the solid image-pick-up element (e.g. line image sensor TCD 106C made by TOSHIBA) is so composed as to obtain an arrangement of picture elements each of which is about 7 .mu.m in size, other colors appear as a fringe on the periphery of a reproduced image when the correspondence of the light image incidenting upon aforesaid image sensor in the example in FIG. 1 described later deviates over a quarter picture elements (approx. 2 .mu.m), for example, a color ghosts in red, blue or other colors appear on the periphery of characters and figures in black. Especially when a deviation of 1 picture element (approx. 7 .mu.m) or more takes place in aforesaid correspondence, the influence is remarkable. For preventing the color ghost, electric corrections have been generally made. However, when the most of color ghosts are intended to be prevented by means of an electric process, the capacity of memory for the process needs to be very large. And, image-wise problems that thickness of line image varies, for example, take place and it is not a perfect one because of the technical difficulties, which represents unsolved problems from the commercializing viewpoint.
The inventor of this invention has made a proposal through Japanese Patent Application No. 239174/1985, as to a means for preventing the deviation between picture elements of image sensors. In the proposal, each of solid image-pick-up elements 51a and 51b is fixed on each of base plates 52a and 52b to be a unit respectively as shown in FIG. 8, and they are capable of being adjusted, as shown in FIG. 7, both in directions to two axes of x and y orthogonalized each other spacially and in rotating directions around x and y axes, thus the units may be adjusted and fixed mechanically. Aforesaid proposal enables each solid image-pick-up element to be adjusted finely for fixing thereof and immediately after the adjustment, the correspondence between elements showed that they were mostly registered. As shown in FIG. 8, however, light-separating prism 54 that is an optical member and is provided behind the condenser lens 53 and solid image-pick-up elements 51a and 51b are mounted respectively on the frame and there are many holding members between them, such as the supporting units adjusted and fixed with adjusting screws which easily cause the deviation in positioning due to expansion or shrink depending on the temperature variation and the screws adjusted improperly and having their plays and errors, and it was not easy to solve the problems of the deviation of picture elements including the stability thereof. Especially when the solid image-pick-up element that is of a mechanical structure is held and fixed by means of precision screws, since a fine adjustment in the order of .mu.m while applying the tightening force of aforesaid precision screws onto the solid image-pick-up element is necessary, it is very difficult to secure the precision. Further, even when the solid image-pick-up element is fixed fairly tightly by using the jig, it easily moves by several .mu.m or more due to the restoration of the distortion upon releasing from the jig after tightening it with the torque for final setting by screws. And even when the image-pick-up element is set precisely within the accuracy of 1 .mu.m, an occurrence of the deviation of several .mu. m or more was observed in the impact test, due to the strain caused by stress in it's parts. Furthermore, the disadvantage of an occurrence of error caused by the coefficient of thermal expansion was observed after the temperature test.
Further, it has been proposed, for fixing the solid image-pick-up element, to fix it by the use of the adhesives in Japanese Utility Model Application O.P.I. No. 57670/1982. This proposal, however, relates to the fixing of a single solid image-pick-up element and it is not for the fixing to the optical member. It is for adjusting/fixing the solid image-pick-up element to the frame and, in this fixing, an amount of the adjustment is compensated by filling the adhesives, therefore, it may not be applied to the image-reading apparatus having a plurality of image-pick-up elements that requires the high precision wherein no deviation for positioning is allowed.